For many decades, conventional motor vehicles have been provided with vacuum boosted wheel braking systems. Before power assisted brakes were used, the brake pedal force applied by the driver acted directly on a master cylinder piston which provided hydraulic pressure applied to brake drum cylinders or disc brake calipers. Many decades ago, a system was developed for providing additional force to apply hydraulic brakes which enabled the operator to use reduced pedal pressure, yet provide strong braking performance. By far, the most commonly used systems today are vacuum booster types. Conventional internal combustion (IC) engines produce a low pressure (relative to atmospheric pressure) in the combustion air intake manifold since a throttle plate in the air induction system restricts air intake flow drawn by the engine. The throttle plate is typically part of a carburetor in older engine designs, or in a so-called throttle body in more modern engines with fuel injection systems. The position of the throttle plate is a primary input in controlling engine power output. The pumping effect of the engine cylinders draw air across the throttle plate which results in a vacuum condition in the intake manifold. In other words, a pressure less than atmospheric is created. A large diaphragm in the booster unit is mechanically connected with the brake's master cylinder piston. The vacuum air pressure is applied to both sides of the diaphragm. When the brake pedal is depressed by the driver, atmospheric air is allowed to enter the booster cavity on one side of the diaphragm. This creates a pressure differential across the diaphragm which results in a net apply force acting on the master cylinder piston in a manner proportional to the actuation force applied to the brake pedal.
The conventional vacuum assisted power brake system has provided outstanding performance. In more recent designs of internal combustion engines, the throttle butterfly valve is removed from the air intake manifold of the combustion air induction system. These engines have their power output controlled by other means, such as through cylinder head valve operation control or by modifying the charge induced by a fuel injection system. Since the throttle butterfly valve is absent in these designs, intake manifold vacuum adequate for brake booster operation is also not available. Accordingly, these engine designs do not provide a convenient source of vacuum pressure for a booster unit used in providing power assist for the braking system.
Various solutions have been considered to address the need for maintaining power assisted braking performance for use with engines using a so-called throttleless-type air intake manifolds. One approach is to provide an external vacuum pump which is belt driven by an engine crankshaft pulley or driven by an electric motor powered from the vehicle's electrical power buss. Such systems require additional components which add cost and complexity to the vehicle.
The present invention seeks to address the shortcomings of the prior art enabling a modified vacuum booster system to be used with an IC engine with a throttleless-type air intake manifold.